Macromolecules in a Solvent

Materials have many properties that are important, scientifically and teclmologically, that do not depend on the details of long-range stnicture. For example, consider a solution of globular macromolecules in a solvent... 

Comput. Phys., 97, 144 (1991). The Electric Potential of a Macromolecule in a Solvent—A Fundamental Approach. 

The entropy of a network-solvent system will increase because of the tendency of the solvent molecules to disperse in the network. This is in analogy to thermodynamics of the dissolution process of macromolecules in a solvent. In reality, it is necessary to take into consideration the additional effect of interaction between polymer segments and solvent molecules, e.g., by introducing an interaction parameter. The dilation gives rise to an elastic response from the network chains which will oppose the tendency for dilation. 

Polymer macromolecules in a solvent may give rather remarkable effects on the fluid behaviour in different flow situations both in the dilute and the non-dilute range. 

Praprotnik M, Delle Site L, Kremer K (2007) A macromolecule in a solvent adaptive resolution molecular dynamics simulation. J Chem Phys 126(13) 134902... 

Viscosity and molar mass measurements for 70 and 71 supplemented with broad H-NMR signals which depended on concentration, temperature, and solvent but independent of NMR frequency, strongly suggested self-association of these macromolecules (in a CHC13 solution). 

The first of these assumptions, generally accepted in macromolecular chemistry [1,3], is correct enough when considering the propagation reaction under copolymerization of the majority of monomers. Simple estimates reported in paper [74] support the correctness of the second assumption. As for the third one, it is true, strictly speaking, only under 0-conditions. The conformational statistics of macromolecules in a thermodynamically good solvent is known [30] to differ from the Gaussian one. Nevertheless, this distinction may hardly influence the qualitative conclusions of the simplest theory of interphase copolymerization. To which extent the account of the excluded volume of macromolecules will affect quantitative results of this theory, may be revealed exclusively by computer simulations. 

The viscosity of the solution is significantly increased when macromolecules are dissolved in a solvent. The specific viscosity of a solution t sp=(ri-r o)lr o expected to increase proportionally to the concentration c. The reduced viscosity rjgp/c still increases with increasing concentration. The data, however, can be extrapolated to zero concentration and results in the intrinsic viscosity, or the viscosity number [77], sometimes also called the Staudinger index... 

Ratio of a dimensional characteristic of a macromolecule in a given solvent at a given temperature to the same dimensional characteristic in the theta state at the same temperature. The most frequently used expansion factors are expansion factor of the mean-square end-to-end distance, Ur = (/o) expansion factor of the radius oj gyration, as = (/0) relative viscosity, = ([ /]/[ /]o), where [ ] and [ /]o are the intrinsic viscosity in a given solvent and in the theta state at the same temperature, respectively. 

The properties of solutions of macromolecular substances depend on the solvent, the temperature, and the molecular weight of the chain molecules. Hence, the (average) molecular weight of polymers can be determined by measuring the solution properties such as the viscosity of dilute solutions. However, prior to this, some details have to be known about the solubility of the polymer to be analyzed. When the solubility of a polymer has to be determined, it is important to realize that macromolecules often show behavioral extremes they may be either infinitely soluble in a solvent, completely insoluble, or only swellable to a well-defined extent. Saturated solutions in contact with a nonswollen solid phase, as is normally observed with low-molecular-weight compounds, do not occur in the case of polymeric materials. The suitability of a solvent for a specific polymer, therefore, cannot be quantified in terms of a classic saturated solution. It is much better expressed in terms of the amount of a precipitant that must be added to the polymer solution to initiate precipitation (cloud point). A more exact measure for the quality of a solvent is the second virial coefficient of the osmotic pressure determined for the corresponding solution, or the viscosity numbers in different solvents. 

As explained earlier (Sect. 1.3.1), macromolecules in a low-molecular-weight solvent prefer a coiled chain conformation (random coil). Under special conditions (theta state) the macromolecule finds itself in a force-free state and its coil assumes the unpertubed dimensions. This is also exactly the case for polymers in an amorphous melt or in the glassy state their segments cannot decide whether neighboring chain segments (which replace all the solvent molecules in the bulk phase) belong to its own chain or to another macromolecule (having an identical constitution, of course). Therefore, here too, it assumes the unperturbed ) dimensions. 

Thus, in small-angle x-ray scattering, measurement of the molecular weight of a macromolecule in concentrated solvent requires knowledge of the preferential interaction parameter. This can be measured by techniques such as differential refractometry, densimetry, and isopiestic vapor phase equilibrium measurements. For densimetry,... 

Lyophilic sols are true solutions of large molecules in a solvent, Solutions of starch, proteins, or polyvinyl alcohol in water are representative of numerous examples. Properties of these solutions at equilibrium (for example, density and viscosity) are regular functions of concentration and temperature, independent of the method of preparation. The solvent-macromolecule compound system may consist uf more than one phase, each phase in general containing both components. Thus, if a solid polymer is added to a solvent in an amount exceeding the solubility limit, the system will consist of a liquid phase (solvent with dissolved polymer) and a solid phase (polymer swollen with solvent, i.e., a polymer with dissolved solvent). 

The curves illustrate two variants of the concentration dependence of the mean size of a macromolecular coil in solution. The example is taken of a macromolecule in a good solvent, so that at low concentrations the size of the macromolecular coil is larger than the size of ideal coil, R2)/ R2)o > 1. 

Plasticizers are generally differentiated as external and internal. The former are bound to the plastics macromolecule as a solvent, by physical (van der Waals) forces. The amount of adsorbed plasticizers is almost unlimited. However, even small amounts of most plasticizers have noticeable effects in plastics. The advantages of external plasticizers consist in the wide variations of both the amounts than can be used and the properties of the bound substances. 

Biopolymer incompatibility is a general phenomenon typical of aU polymers. Biopolymer incompatibility occurs even when their monomers would be miscible in all proportions. For instance, sucrose, glucose and other sugars are normally cosoluble in the common solvent, water, while different polysaccharides usually are not miscible. The transition from a mixed solution of monomers to polymers corresponds to the transition from good to limited miscibility. Normally, a slight difference in composition and/or structure is sufficient for incompatibility of macromolecules in common solvent (Tolstoguzov 1991, 2002). Compatibility or miscibility of unlike biopolymers in aqueous solutions has only been exhibited by a few biopolymer pairs (Tolstoguzov 1991). 

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